Method of forming induction motors



5; R. BERGM'AN us'rnon OF FORMING INDUOTIONIOTO'RS an ina med Nov. 29, 1924 Fig. I

Inventor: I Sven R. Bev'gmevn, y v His Attorney com leted;

PATENT OFFICE.

SVEN 3. 3mm, 0] NAHANT, MASSACHUSETTS, ASSIGNOB TO GENERAL ELECTRIC A CORPORATION 01' NEW YORK. I

METHOD 0! FORMING INDUCTION MOTORS.

Original application'fled Ievember 99, 1924,!61'181 No. 759,993. Divided and this application filed Iebruary 87, 1928.

My invention relates to induction motors squirrel cages on the rotors of such motors.

The present apglication is a division of my application, erial No. 7 52,993, filed Nov.. 29, 1924.

It is well known that in order-that an induction motor should start under load without an excessive current flow, it is necessary that the seconda circuit shall pos-- sess a high resistance, an on the other'hand, that when the motor is up to speed the re'-' sistance and the reactance of the secondary circuit should be low in order to secure eflicient o eration.

It has con proposed heretofore to provide the, secondary member of an induction motor with two squirrel cage windings, one

of hi h resistance and low reactance andi the ot er of low resistance and high relictanc e. When starting with such an arrangement, the frequency of the secondary currents is high and t e high resistance winding will car the greater part of the load, but when t e motor is up to speed, c

the fre uency of the secondary currents is low an the low resistance winding will carry the load.

My invention has for its ob'ect a novel method of forming the rotor o amotor of the above described type. For a better understanding of my invention, reference may be had to the following description taken in connection with the accomparrtilying drawing, in which Fig. 1 is a .view pa y in'section of a mold and a rotor, the rotor representing its condition after the first ste of my new method has been ig. 2 isa'view artly in section of t e completed rotor and ig, 3 isan'end view of the rotor of 'Fig. 2.

Referring to the drawing, 1 is the magnetic core of an induction motor having relativel deep conductor receiving openings 2 andsliallow conductor receiving openings 3. In order to cast'squirrel cage windings in these conductor receiving openings, the core 1 is placed in a suitable mold formed in such a manner that the slots will be entirel filledwith conductor ortions" united at each end b a single en ring. I then, by a suitab e tool, separate the single end ring into two component parts, one of smaH cross section'and high resistance connecting Serial No. 257,903. r the conductors in the shallow slots with the conductor portions in they tops of the deep slots and the other of large cross section and low reslstanceconnecting together the conductor portions in the bottomsof the dee slots. In the casting operation I prefera ly employ a mold comprising end flange portions 4 and 5 and a cylindrical portion .6; The cylindrical portion 6 embraces the outerperiphery of the core member and the flange portions 4 and 5 are fastened together as bly bolts 7 so as to firmly clamp together the aminations forming the core 1. These flange portions engage the laminationsat their outer peripher and each is cut away so as to have forme therein two cylindrical grooves 8 and 9. The groove 8 is narrow, whereas the groove 9 is wide, for a purpose which will be hereinafter explained. The V flange has an opening 10 therein through which molten metal may be poured to form conductors in the conductor receiving openings 2 and 3 and end rings in the grooves 8 and 9 integral with the conductors.

by any suitable method. I have chosen to illustrate the centrifugal method of the Reist and Maxwell PatentvNo. 1,190,009, dated July 4, 1916. The mold and core are rotated as a unit in any suitable manner.

. For this purpose, there is shown a' mandrel .11 fastened 1n the shaft receiving opening 12 of the core 1, the mandrel having mounted thereon a pulley 13, the whole 'being rotated by means of a beltl i. While the core and mold are bein rotated, metal is poured through the opemng 10. ,This metal flows down the large portions 15 of the deep conductor receiving'openings '2' and also partially down the shallow conductor receivin openings 3 and partially down the sma portion 16 of the deep conductor receiving openings 2. Such metal after flowing down through the portions 15 of the openings 2 also flows u the openings 3 and the portions 16 of t e openings 2 uniting with the metal which flows down these 0 enings."

Molten metal. also fills the cy indrical grooves 8 and 9 forming end rin s of large cross section, one at each end- 0 the rotor core. Metal also flows into the intermediate long, narrow portions 17 of the deep conductorreceiving openings, which unites the conductors in the portions 15 and 16 of these The squirrel cage windings may be cast I openings into a single conductor. Sufiicient metal is poured into the mold to form conductors in the slots 2 and 3 and end rings in the grooves 8 and 9 Rotation of the mold and core is continued until the molten metal has congealed, When the mold and parts are sufficiently cool to handle, the bolts 7 are removed, thereby permitting the parts at, 5 and 6 of the mold to be removed. The conductors with their integral end rings firmly clamp the laminations together. After the rotor is removed from the mold, the end rings which were formed in the grooves 8 are machined in any suitable machine tool, so as toseparate each of the large end rings into two separate, concentric end rings 18 and 19. The end rings 18 thus formed are of small cross-section and are integrally connected to the conductors formed in the shallow conductor receiving openings 3 and the conductors formed in the portions 16 of the deep conductor receiving openings 2'and form with these conductors a high resistance, low reactance squirrel cage winding. The end rings 19 are of large cross-section and are integrally connected with the conductors formed-in the portions 16 ot the deep conductor receiving openings 2 and form therewith a low resistance, high reactance squirrel cage winding.

I have shown the cylindrical grooves 9 of the flange portions of the mold rovided with rectangular projections whic act as cores to form longitudinally extending s aces 20 in the end rings 19. These spaces f drm fan blades 21 on these end rings. If desired, these projections may be omitted from the mold and the. metal of the end rings machined away to form fan blades after the-squirrel cages have been cast, or if desired, the fan blades may be omitted entirely.

In order to make a double squirrel cage motor, which can be thrown directly on a source of power and which will start under load with a small current consumption, it is necessary that the low reactance winding be of high resistance. I have found, however, that the smallest diameter ofconduc-' tor receiving opening into which metal will flow and form a continuous conductor therethrough is'about 2/10 of an inch. A squirrel cage winding formed of conductors of this size with end rings of large cross section united to both squirrel cages, is too low a resistance to effect successful startin under the above conditions. I conceived -t e idea of placing a considerable portion of the resistance of the low reaetance squirrel cage winding in the end rings thereof, making it possible to use sufficiently large slots for the conductors of this winding, so that it could readil be cast. In order to get the resistance 0 this end ring sufliciently high fer this purpose, I form it as explained above, that is, by casting it integral with the end ring for the low resistance winding and then separating it therefrom by a machining operation.

The deep conductor receiving openings 2,

as explained above, have a large portion 15 at the bottom thereof and a small portion 16 at the top thereof, joined by an intermediate long, narrow portion 17. When the squirrel cage windings are cast, the conductors substantially completely fill these openings 2. The squirrel cage Winding formed with the conductors in the small portion 16 of the slots is (if-high resistance for the reason pointed out above. It is of low reactance, because flux will not pass above it. On the other hand, the winding formed of the conductors in the larger portion 15 of the slots is of low resistance since not only are the conductors of large cross section, but so are the endrings joining them. This winding is of high reactance because of the narrow air gap provided above it by the long, narrow portion 17 of the slots, acrosswhich flux will pass when the motor is starting with little or no fiux passing under this winding. I have found that the resistance of the low reactance winding should preferably be three times that of the higher reactance winding, so that when the motor is operating at normal speed and under load, this high resistance winding will carr the maximum current consistent with goo efficiency, obtaining at the same time the best possible power factor. The squirrel cage windings are preferably cast out of aluminum, but any other suitable metal may be used. If desired, the shallow conductor receiving openings 3 may be omitted, and the high resistance winding all placed in the portions 16 of the slots 2. I aim in the appended claims to cover all modifications of my invention which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. The method of forming an induction m tor squirrel cageon a magnetic core having deep conductor -receiving openings therethrough, which consists in casting conductors in said conductor receiving openings and integral end rings of large cross-section, one at each end of said core, and thereafter separating each of the end rin 5 into separate rings, one formed with t e ortions of the conductors in the top of t e eonductor receiving openings and the other formed with the ortions of the conductors in the bottom 0 the conductor receiving openings.

2. The method of forming an induction motor uirrel cage on a magnetic core having relatively deep conductor receiving openings therethrough, which consists in casting conductors in said conductor receiving openings and integral end rings of large crosssection, one at each end of said core, and' thereafter separating each of the end rings 5 into concentric rings, one of relatively hi h resistance formed with the portions of t e conductors in the top of the conductor receiving openings and the other of relatively SVEN R. BERGMAN. 

